Method of making loud-speaker diaphragms



Nov. 25, 1952 J. B. BRENNAN 2,619,012

METHOD OF MAKING LOUD-SPEAKER DIAPHRAGMS Filed Aug. 5, 1947 Patented Nov. 25, 1952 UNITED STATES PATENT OF FICE "METHOD 0F -MAKING LOUD-'SPEAKER DIIHRAGMS 2 Claims.

.This invention relates to: method rof making loud speaker diaphragms andv the'. like and 'particularlyto the deposition of fibrousmaterial froma suspension to forma `blank and to compressing the formed blank to complete the article.

One of the' objects of the present invention is to lprovi-de a method of forming loud speaker diaphragms and the like in which a blank is formed by depositing Afibrous material and is thereafter pressed to compress the deposited :fibers and to shape the blankainto the desired nished shape. According to one feature of the invention, the ange portion of the diaphragm is formed flat in the blank and is drawn into one or moreannular corrugations during the pressing operation. I nave found tnat this increases the flexibility of the flange portion of the diaphragm without substantially effecting its strength.

vAnother object is to providea method of making diaphragms and the like in which bers are depositedfrom a suspension, such as an aqueous suspension, under super-atmospheric pressure. Preferably, the fibers are deposited on a porous mold plate which is subjected to vacuum on its lowerside so that the fibers will be accreted rapidly. If desired, a plunger member may be employed to produce the super-atmospheric pressure in the suspension and may also serve to compress the deposited'bers against the mold plate to reduce the moisture content and increase the density.

.The'above and other objects and advantages of the invention will be more readily apparent from the following description when read in connection with the accompanying drawing, in which- Figure 1 -is a sectional View through a pressing mold embodying the invention;

Figure 2 is a similar view through a fiber depositing'apparatus; and

Figure 3 vis a partial enlarged section through a mold part.

In carrying out the invention, loose fibers, such as cotton, kapok, wood bers, or the like, are deposited on a mold plate which may roughly approximate the desired nished diaphragm shape to form a relatively soft blank. The blank so formed is' thereafter pressed in a two-part mold to'compress the bers to the desired density and to bring the blank to the desired nished shape. Preferably, portions of the blank, such as its peripheral iiange portion, are actually drawn during the pressing operation to stretch the blank. I have found that this substantially increases the exibility of the blank flange portion without adversely affecting its strength.

Figure 2 illustrates an apparatus for forming blanks by depositing bers from an aqueous suspension. As shown, the apparatus comprises a hollow housing IB formed in its lower part with an outlet connection II through which liquid may drain and which is connected to a source of suction, such as a vacuum pump. The housing carries a porous mold plate I2 which is formed with a downwardly concave generally conical central portion and a ilat ilange portion. An upwardly extending rim I3 is secured above the mold plate adjacent the periphery thereof and forms with the mold plate a receptacle to receive a measured quantity of an aqueous'ber suspension. it will be seen that by filling the rim to its upper edge, a predetermined quantity of suspension'will vbe held above the moldplate so that a fibrous article ofv predetermined thickness will be'formed. It is noted that a greater quantity of suspension will lie over the central portion of the mold plate than over the flange portion so that fibers will be deposited to greater thickness in the central part than at the edge. This produces an article which is thicker and more rigid in its center body portion than-in its iiange, which is a highly desirablel construction in loud speaker diaphragms.

A plunger indicated generally at I4 is formed to iitr slidablywithin the rim I3 and ismovable toward the mold plate I2 to force the suspension therethrough. .The plunger, as shown, includes a central conical portion I5 which is complementary to the central conical portion of the mold plate.

In forming a blank with the apparatus as so far described, the rim I3 may be lled with aque-1 ous suspension of iibrous material and the plunger may be forced downwardly in the rim while the lower surface of the mold plate is subjected to vacuum through the connection II. Due to the action of the vacuum and the super atmospheric pressure produced by the plunger, the liquid will be forced rapidly through the mold plate leaving the bers deposited on the upper surfaces of the mold plate. If desired, the plunger may be forced down against the bers to compress them against the mold plate thereby to squeeze Water from the deposited bersand partially to compress the deposited fibers. Upon completion of this operation, the plunger may be raised and the blank formed by the deposited fibers may be removed from the mold plate.

The blank formed-as described above may then, be subjected to a pressing and forming operation in the apparatus, as shown in Fig. 1. .This appa'- ratus comprises a two-part mold having a lower female part I6 whose upper surface agrees with the desired finished shape of the diaphragm. The mold part I6 corresponds with a male mold part Il which is preferably hollow and is formed of a porous material. The mold part I I is open at its enlarged upper end and is adapted to t against a mold plate I8 which serves to close the upper end of the part I'I. The mold plate may in turn fit against a plunger I9 which is adapted to be moved vertically toward and away from the lower mold part I6. The interior of the hollow mold part I1 may be subjected to suction through a suction passage 2I communicating therewith and may be heated by one or more electric heating elements 22 mounted between the hollow mold part and the plate I8.

For supporting the porous mold part I'I and for closing its exposed upper edge to prevent flow of air therethrough, a mounting ring 23 is provided. The ring 23 may be of solid metal, or the like, and ts closely against the outer edge of the porous mold part, as shown. At several points in its circumference, the ring 23 is formed with openings through which fastening plates 24 may extend into an annular groove 25 in the edge of the mold part. The plates 24 may be held by screws 26 threaded into the edge of the plunger I9 so that the mold part I'I and the plate I8 will be drawn up tight against the plunger.

The relatively soft blank as formed on the apparatus of Fig. 2 may be placed in the two-part mold of Fig. 1 and the heated upper mold part may be pressed down against the blank while subjected on its interior to suction. Thus, the blank is compressed to form a completed diaphragm as indicated at 27 which is in the desired finished shape. Due to the combined action of heat and suction, the moisture in the blank will be rapidly dried out so that the blank may be finished quickly. After pressing, the blank is coated or imf pregnated with lacquer or like lling materials or, if preferred, the lacquer could be applied thereto before pressing the blank.

According to one feature of the invention, the flange portion of the diaphragm is drawn into one or more annular corrugations during the pressing operation. As shown in Fig. 1, both of the mold parts have peripheral flange portions which are annularly corrugated.. When the blank with its initially at ange portion is pressed into the two-part mold, the flange portion will be drawn causing the fibrous material actually to ow to form the annular corrugations. I have found that this provides a flange of extremely high ilexibility and of maximum strength. The reason for this may lie, at least partially, in the fact that radial flow of the bers in the blank to form the corrugations causes the fibers to become radially aligned so that maximum strength in a radial direction is produced.

According to one feature of the invention, either or both of the porous mold parts I2 and I'I may be formed of particles of sintered material. Relatively ne particles of non-corrosive material, such as particles of stainless steel, or bronze, or a mixture thereof, of substantially uniform size are placed in a mold and are sintered to bind the particles together in a porous structure. It is important that the particles be of substantially uniform size and that their neness be such that when they are sintered together, the spaces or openings between particles will be of smaller size than the fibers. Otherwise the fibers will enter partially into the spaces between the particles and stick therebetween. A mold part, formed as described above, is relatively inexpensive, possesses a high strength and rigidity, and is extremely porous throughout. If desired, different degrees of porosity can be provided in different portions of the mold to vary the thickness of the deposited bers in different mold portions by employing particles of different size to form the different portions of the mold or by compressing the particles to different degrees during the sintering.

For the pressing mold as shown at I'I a smooth surface is required, particularly in the ange portion of the mold so that the blank can slip over the mold during the drawing operation. I have found that a surface of the necessary smoothness can be produced by machining the mold part after sintering. I have found that the surface when machined with a sharp cutting tool or when ground with a wheel will provide the necessary smoothness without loss of porosity and without any subsequent treatment, such as etching. In the alternative, the surface of the mold part may be covered with a fine porous sheet. such as perforated metal or Woven wire, as illustrated in Fig. 3 in which the sintered metal mold part is shown at 28 having one surface thereof covered by a ne woven wire screen 29. When this construction is employed, the screen may be pressed or formed to the same shape as the mold part and may be simply laid over the mold part and clamped thereto at its edges. The screen is preferably of a iineness such that the fibers cannot enter its interstices and provides a surface sufficiently smooth so that the fibrous blank can slip over it during a pressing or forming operation. When such a screen is employed, the sintered metal mold part can be made of larger or courses particles and does not require any surface finishlng.

While the invention has been particularly described in connection with the formation of loud speaker diaphragms, it will be understood that in many of its yaspects it is applicable lto the formation of articles of different character, and, therefore, it is not intended to limit the invention to the exact procedures 'and structures described herein nor otherwise than by the details of the appended claims.

What is claimed is:

1. The method of making loud speaker diaphragms and ythe like which consists in depositing fibrous material from a suspension to form a diaphragm blank having a generally conical body portion of substantially the desired finished shape and a fiat peripheral flange, and compressing the body portion of the blank at an elevated temperature while maintaining the body portion in said generally conical form, and simultaneously drawing the flat peripheral flange into an annular corrugation. Y

2. The method of making loud speaker diaphragme and the like which consists in depositing fibrous material from an aqueous suspension to form a diaphragm blank having 'a generally conical body portion of substantially the desired nished shape and a fiat peripheral iiange, and compressing the body portion of the blank lat an elevated temperature and subjecting at least one face of the blank to ithe action of suction while maintaining the body portion in said generally conical form, and simultaneously drawing the at eripheral flange into an annular corrugation.

JOSEPH B. BRENNAN.

(References on following page) REFERENCES CITED Tnewfollowing references are of record in the le of this patent:

jUNITED STATES PATENTS Number 208.091 380,099

Name Date House Sept. 17, 1878 Duncan 1 Mar. 27, 1888 Baum May 1, 1928 Mason July 7, 1931 Sutherland Oct. 25, 1932 Brennan Aug. 22, 1933 Ledeboer Jan. 30, 1934 Hawley Dec. 11, 1934 Number Number 

